Proton Beam Therapy for Oncological Applications

Proton beam therapy (PBT) harnesses the unique depth‐dose characteristics of accelerated protons to deliver highly conformal radiation to tumours while minimising exposure of surrounding healthy tissues. The hallmark of PBT is the Bragg peak, a phenomenon whereby protons deposit the bulk of their energy at a narrow depth, allowing steep dose gradients beyond the target. Clinical adoption has grown globally over the past two decades, with centres now treating a broad spectrum of malignancies, including paediatric cancers, head and neck tumours, central nervous system lesions and selected thoracic and abdominal neoplasms. Advances in beam delivery techniques, such as pencil beam scanning and intensity‐modulated proton therapy (IMPT), have further refined dose sculpting and enabled complex treatment geometries. Biological advantages stem from the variable relative biological effectiveness (RBE) of protons, which can enhance tumour cell kill at the distal edge of the beam. Emerging research into ultrahigh dose rates or “FLASH” irradiation suggests additional normal tissue sparing. Current challenges include managing range uncertainties due to anatomical changes and inter‐fraction motion, ensuring robust treatment planning and integrating adaptive strategies. The ongoing development of imaging‐guided delivery, automated plan adaptation and novel beam‐modulation devices promises to extend the clinical reach and cost‐effectiveness of proton therapy, underpinning its role in precision oncology.

Research from Nature Portfolio

Recent studies have introduced a momentum cooling approach in cyclotron‐based proton facilities to narrow the beam’s energy spread without substantial losses. By inserting a bespoke wedge in the energy selection system instead of conventional slits, researchers achieved up to a twofold increase in transmission for low‐energy beams and demonstrated the concept in an eye‐treatment beamline. Modelling of a gantry equipped with momentum cooling predicts nearly a hundredfold improvement in transmission for 70 MeV beams. This advance could enable ultrahigh dose rates, reduce treatment times and open new clinical indications by lowering operational costs and enhancing the feasibility of FLASH dose delivery.

Proton Beam Therapy for Oncological Applications publication trend

The graph below shows the total number of articles in proton beam therapy for oncological applications across all publications each year (not limited to Nature Index journals).

Technical terms

Bragg peak: The sharp maximum in energy deposition by protons at a specific depth in tissue, enabling precise tumour targeting.

Relative biological effectiveness (RBE): A ratio expressing the effectiveness of protons compared to reference radiation (typically photons) in producing a biological effect.

Pencil beam scanning (PBS): A delivery method that scans a narrow proton beam spot across the tumour in three dimensions for highly conformal dose distributions.

Intensity‐modulated proton therapy (IMPT): An advanced form of PBS that modulates beam intensity and energy layer by layer to optimise dose throughout complex tumour volumes.

Momentum cooling: A technique to reduce the energy spread of a proton beam by passing it through a material wedge, enhancing transmission and dose rate.

FLASH effect: A phenomenon whereby ultrahigh dose‐rate irradiation appears to spare normal tissue while maintaining tumour control, under active investigation.

References

1. Demonstration of momentum cooling to enhance the potential of cancer treatment with proton therapy. Nature Physics (2023).
2. Comparative assessment of radiation therapy–induced vasculitis using [18F]FDG-PET/CT in patients with non-small cell lung cancer treated with proton versus photon radiotherapy. European Journal of Nuclear Medicine and Molecular Imaging (2023).
3. A review of proton therapy – Current status and future directions. Precision Radiation Oncology (2022).